1. Field of the Invention
The present invention relates to an electrically conductive member for use in electrically connecting a plurality of solid oxide fuel cells to assemble a fuel-cell stack, and a fuel-cell stack using the same.
2. Background Art
Solid oxide fuel cells are expected as fuel cells that are operated at elevated temperatures (800 to 1000° C.) with high efficiency. The solid oxide fuel cells are usually used in the form of a structure called a stack comprising a plurality of solid oxide fuel cells (one fuel cell unit being hereinafter often referred to as “fuel cell”) which have been electrically connected in series and/or parallel and bundled.
In forming the stack structure, a plurality of fuel cells should be electrically connected, and, to this end, a felt of nickel has been used as an electrically conductive member. For example, Japanese Patent Laid-Open No. 25999/1999 proposes a fuel-cell stack using an electrically conductive member formed by folding a metallic fiber assembly composed mainly of nickel, that is, an electrically conductive sheet formed of a nickel felt, a plurality of times. According to this publication, the claimed advantage of the electrically conductive member having this construction is to have cushioning properties satisfactory for stress relaxation between fuel cells.
So far as the present inventors know, however, there is still room for improvement in cushioning properties of the felt structure. The nickel felt is highly elastic. Since, however, it is formed of a plurality of fibers which have been entwined with each other, once compressive force is applied, the elasticity or restoring force becomes often unsatisfactory. As a result, after the felt structure is once placed between fuel cells and is pressed to a given shape, it is difficult to re-regulate the thickness in the regulation of the spacing between fuel cells. This is because, in the re-regulation of the spacing between the fuel cells, waste fibers disadvantageously occur, leading to a fear of causing energization across the electrodes. Further, after baking or power generation is once carried out, fibers in the nickel felt become complicatedly entwined with each other. In addition, the contact area between the fibers is so large that the fibers are disadvantageously integrally sintered in a hard state, making it difficult to replace a part of the fibers after that. As a result, the maintainability and the like are poor, and, thus, there is room for improvement.